Fluorine-Doped CdS Enables Oriented Growth and Defect Suppression in Sb₂Se₃ Solar Cells with High Conversion Efficiency

Antimony selenide (Sb₂Se₃) as a quasi-1D absorber holds promising potential in photovoltaics, but its practical efficiency remains far below the theoretical limit due to challenges such as deep-level defects and difficulties in crystal orientation control. High-efficiency devices typically use cadmium sulfide (CdS) buffer layers made by chemical bath deposition (CBD), but achieving low-defect, stable CdS films is challenging. In the superstrate configuration, the interfacial quality of CdS is recognized as a critical factor influencing the oriented growth of Sb₂Se₃ and overall device efficiency. This study pioneers the use of fluorine (F)-doping to modulate the microstructure and surface energy states of CBD-CdS, aiming to passivate sulfur vacancies and expose non-polar surface planes (100), thereby inducing preferential orientation of Sb₂Se₃ along its high-mobility growth direction. Furthermore, effective passivation of sulfur vacancies by F ions substantially improves Sb₂Se₃ growth kinetics. The optimized films exhibit a reduced Se/Sb ratio (from 1.98 to 1.63), a three-order-of-magnitude decrease in defect capture cross-section (from 10⁻¹⁷ to 10⁻²⁰), and achieve an efficiency of 9.30%, representing an 18% improvement over the control device. The work proposes a low-temperature, scalable interfacial engineering strategy with broad applicability, offering new insights into defect suppression and crystal orientation optimization for enhanced photovoltaic performance.